1. Field Of The Invention
This invention relates generally to carrier tapes for semiconductor devices and more particularly relates to an improved tape bonded semiconductor device structure using semiconductor chips having denser bonding pads than envisioned by the prior art and to a method of connecting carrier tapes with dense input/output leads to the improved semiconductor chip.
2. Prior Art
The semiconductor industry is driven by automation and smaller packages and is presently producing devices with the so-called TAB, i.e. Tape Automated Bonding, technique in which the tape, is comprised of an insulating carrier, formed of a material such as polyimide or the like, carrying a multiplicity of thin metallic films which extend beyond openings in the polyimide to form what are generally called tape leads or fingers. The metallic film, usually a copper based material, is generally very thin, typically 0.5 to 3 mils in thickness. Generally, to form the tape the metallic film is laid down on the polyimide substrate and the fingers, i.e. the leads, formed insitu by etching or other suitable forming techniques. Following this, a portion of the carrier is removed, by etching or the like, under the inner and outer tips of the fingers. The finished tape is used by precisely aligning each inner tip with a respective bonding pad on a semiconductor chip and bonding the chip to the pad by thermo compression. In TAB automated bonding this thermo compression bonding is performed by a single bonding tool in a method called gang bonding. Similarly, the outer tip of each finger is bonded for example, to a respective lead on a so-called lead frame. Such lead frames are formed of metal substantially heavier and stiffer and are designed to be self supporting and to extend through the exterior of the package.
In the past, most of TAB tapes were formed with a single metallic foil on one side of the insulating carrier film. As chips became more complex, and used double rows of bonding pads, industry responded by placing a second metallic film on the opposite side of the insulating carrier so that connections could be made to the two rows of bonding pads on the chip. This necessitated complex alignment techniques to assure that after etching of both metallic film the metallic fingers formed on each side of the carrier were properly aligned with respect to one another and were of the proper length. This in turn necessitated the use of complex techniques to remove the selected portions of the insulating carrier itself from between the metallic films. This caused the tape, for such designs, to be very expensive and quite difficult to make. Moreover because of the thickness of the fingers and the manner of formation of the double-sided TAB tape it was necessary to offset the pads in the second or inner row of bonding pads on the chip so that they were aligned with the space between the pads of the outer row, i.e. staggered. Still further, the construction did not permit the use of more than two rows of bonding pads on the chip.